Traditionally there are two options for handling encumbrance in fantasy roleplaying games. They both suck. The first is to count up the weight in pounds of every item a character wears and use their Strength score to figure out if the total is too much. The trouble is that this certainly prevents people carrying stacks of rocks or water but normally allows an average person to carry twelve longswords without difficulty. It encourages thinking like "Well, longbows only weigh three pounds so I can easily carry that, and six quivers of arrows, and my armor, and a sword and shield, and a backup mace, and my backpack..." and nothing but silliness ensues. The alternate option is to simply ignore encumbrance and not handle the issue at all. I think counting by pounds actually makes things worse than just hoping that people will be reasonable so in most of my games characters just carry around whatever they like.
One of the things I don't like about that is that it makes being a big strong adventurer not mean much. If the stick armed nerdy wizard can carry around just as much as the gigantic thug then you really lose any sort of benefit for being strong. I like the idea that it is a disadvantage for people to have low stats of any sort. Not that I want to make low stat untenable but I do like the idea that it makes a difference; I want it to be the case that a caster with a high Strength feels like that choice wasn't utterly wasteful. I don't mind that most thugs should be strong and fast and most casters should be clever and wise but the choice should at least have some drawbacks. Tradeoffs are the key to fun decisions.
Hence my solution: In SkyRPG Strength is going to determine how much armour and weapons will slow you down in combat. Armour will probably weigh between 1-5 and weapons between 2-4 with Strength scores ranging from 3 to 10. The formula would be simple: Add up the total weight of armour and weapons worn and compare it to your Strength. If your weight is higher than your Strength you lose one space of movement (from a starting value of 6) for each point you are over. The idea is that someone who really ignores Strength will be limited in what they can carry - probably just a single one handed weapon and leather armor. On the other end of the scale is someone with maximum Strength who can wield a gigantic two handed weapon and full plate.
It is possible to stuff someone who isn't very strong inside heavy armour, hand them a sword and shield, and have them be tough but they will barely be able to move about. This means that adventurers who want to be mobile and be able to climb things and such will either be lightly equipped or massively strong but a regular dude can slap on full plate for a pitched battle and have things make sense. I wanted armour to make sense from a historical perspective (everybody who can afford to go to a battle in heavy armour does) but not make it mandatory for adventurers.